Revert "Move ExtensionCache to //extensions"

extensions/browser/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 
 # GYP version: extensions/extensions.gyp:extensions_browser
 source_set("browser") {
   sources = [
@@ skipping 408 matching lines @@
       "script_executor.cc",
       "script_executor.h",
       "stash_backend.cc",
       "stash_backend.h",
       "state_store.cc",
       "state_store.h",
       "suggest_permission_util.cc",
       "suggest_permission_util.h",
       "uninstall_reason.h",
       "update_observer.h",
-      "updater/extension_cache.h",
       "updater/manifest_fetch_data.cc",
       "updater/manifest_fetch_data.h",
-      "updater/null_extension_cache.cc",
-      "updater/null_extension_cache.h",
       "updater/safe_manifest_parser.cc",
       "updater/safe_manifest_parser.h",
       "url_request_util.cc",
       "url_request_util.h",
       "value_store/leveldb_value_store.cc",
       "value_store/leveldb_value_store.h",
       "value_store/testing_value_store.cc",
       "value_store/testing_value_store.h",
       "value_store/value_store.cc",
       "value_store/value_store.h",
@@ skipping 34 matching lines @@
       ]
     }
   }
 
   if (is_win) {
     cflags = [
       "/wd4267", # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     ]
   }
 }